1. Field of the Invention
The present invention relates to an electron beam irradiation apparatus and irradiation method for performing electron beam irradiation so as to carry out a process, such as cross-linking or curing of a coating formed of, e.g., a printing ink, paint, an adhesive, a pressure sensitive adhesive, or a hard protective film, which is formed on a target object, such as a display unit, optical disk, glass lens, or ID card; or a process, such as sterilization or modification of an object.
2. Description of the Related Art
Many techniques using electron beam irradiation have been proposed as means for carrying out a process, such as cross-linking, curing, or modification of a coating formed of, e.g., a paint, an adhesive, a pressure sensitive adhesive, or a hard protective film, which is disposed on a substrate (for example, Jpn. Pat. Appln. KOKAI Publication No. 2-208325). When a process using electron beam irradiation takes place, electrons are accelerated by an acceleration voltage within a vacuum, and an irradiation target placed within a vacuum or inert gas atmosphere is irradiated with the accelerated electrons.
Processing techniques using electron beam irradiation have many advantages, such that an irradiation target is far less heated, no organic solvent needs to be used, and no curing initiator is necessary.
However, the technique disclosed in the publication described above needs an electron beam irradiation tube of a drum type, and problems thereby arise, as follows. Specifically, such a large electron irradiation tube is operated at a high acceleration voltage, which requires a strict X-ray shield. Further, a large amount of inert gas, such as nitrogen gas, needs to be supplied, so that the oxygen ratio in the atmosphere around an irradiation target is reduced to prevent inhibition of curing by oxygen. As a consequence, the conventional electron beam irradiation apparatus becomes very large in its own size with a large weight. In addition, an electron beam at a high acceleration voltage may cause deterioration, such as yellowing, of some substrates.
As a technique for preventing an increase in the size of the entire apparatus, Jpn. Pat. Appln. KOKAI Publication No. 9-101400 discloses an arrangement in which a transfer system for an irradiation target is modified. In this arrangement, however, since an apparatus having a load-lock chamber is further enveloped within a shield chamber made of lead, the entire apparatus inevitably ends up being still large.
Jpn. Pat. Appln. KOKAI Publication No. 7-019340 discloses a vacuum chamber for ion beam irradiation arranged for the purpose of decreasing the size and contamination, which can actually realize a compact vacuum chamber. This technique, however, is not directed to electron beam irradiation, and thus includes nothing about an X-ray shield. Accordingly, this technique does not solve the problems described above in relation to electron beam irradiation apparatuses, to which the present invention is directed.
U.S. Pat. No. 5,414,267 discloses a technique for downsizing an electron beam irradiation tube and decreasing the acceleration voltage, in which the material of an electron beam irradiation window is modified to realize a high transmittancy for an electron beam even at a low acceleration voltage. Since this technique can thus downsize an electron beam irradiation tube and decrease the acceleration voltage, the amount of X-rays generated from the electron beam irradiation tube is smaller, which allows use of stainless steel in place of lead as an X-ray shield material. Further, since the acceleration voltage to draw out an electron beam is low, a substrate is less affected.
However, since this technique still needs to use an X-ray shield, an inert gas, and a vacuum, the entire apparatus inevitably ends up being large. Further, this publication only discloses a complicated and large apparatus structure including a transfer mechanism prepared for an irradiation target, such as a sheet or cable. Accordingly, as regards an apparatus for performing electron beam irradiation on a number of single articles, this publication does not suggest anything about downsizing or simplifying such an apparatus, or reducing the cycle time for processing an irradiation target.